1. Field of the Invention
The present invention relates to mirror-embedded optical waveguides and fabrication methods thereof, which offer excellent characteristics in terms of cost, mass production and reliability.
2. Description of Related Art
With recent development of information and communication technology typified by the Internet as well as dramatic increase in processor speeds, there has been growing demand for high volume data transmission such as image and motion video. In such high volume data transmissions, there is demand for transmission rates of 10 Gbps or more as well as small effect of electromagnetic noise. Among such high-speed communications, optical transmissions, which are not affected by electromagnetic noise, have shown great promise. In this context, conventionally employed electrical transmissions using metal cables and wiring are being replaced by optical transmissions using optical fibers and waveguides.
Mainly for reducing mounting cost in such optical transmission systems, there have been proposed an optical waveguide which mounts therein a photonic device (such as a surface light emitting device and surface light receiving device) in parallel to its core as shown in FIG. 4. FIG. 4 is a schematic illustration showing a cross-sectional view of a conventional optical waveguide having a photonic device mounted thereon.
In this technology, the optical path needs to be deflected approximately 90° in order to optically couple the core and photonic device. A means for realizing this is to form a V-groove in the core by dicing or the like and to fabricate a mirror on an angled surface of the V-groove. For example, such a mirror is provided by reflection at the bare angled surface formed in the waveguide and, in this case, its reflectivity is determined from the refractive index difference between air and the waveguide (core) material. Another method of forming such a mirror is to form a metal film on the angled surface by vapor depositing a metal such as gold (e.g., see JP-A Hei 10 (1998)-300961).
However, the mirror utilizing the bare surface cut by dicing or the like has a surface roughness (projections and depressions), and therefore has a problem of increased light reflection loss (mirror loss) due to degraded reflection efficiency.
On the other hand, the mirror provided by the metal-deposited surface has a cost problem because the number of waveguides loadable in a vapor deposition chamber becomes limited with increasing size of the waveguide. Also, it requires some form of mask for masking undesired portions. Such use of a mask presents problems of increased cost and resolution limitation. Furthermore, a vapor-deposited metal film generally has a poor adhesiveness to an optical waveguide material, thus posing a problem of peeling. When light is incident on and reflected by the metal film, an adhesive layer such as TiO2 can be sandwiched between the metal film and optical waveguide material in order to improve the adhesiveness therebetween. However, when light is incident on and reflected by the core-side (waveguide-side) surface of such an above-described mirror of an optical waveguide, the light passes through such a TiO2 adhesive layer, thus causing a problem of reduced reflectivity.